The proposal intends to investigate the zone of marginal ischemia following acute coronary ligation in primates. These investigations will include: 1) Electron microscopic study of sections of myocardium from areas of infarction, areas of recovery, recovery after a 2-hour period of reperfusion and areas of normal heart muscle. This will allow more precise definition of ultrastructural changes which occur in myocardium in the apparently recovered zone following reperfusion. 2) Infarcted, recovered and normal zones of left ventricular myocardium will be determined in baboons who have had coronary reperfusion after varying periods of ligation by unipolar ECG mapping. Animals will then be sacrificed, the zones excised, homogenized and aliquots taken for determination of cyclic AMP, ATP, phosphodiesterase and adenyl cyclase. 3) Six animals will have acute coronary ligation for 1/2 to 4 hours after having been injected with tagged autologous platelets. Infarcts will be mapped and then animals sacrificed, the electrically determined area of infarction excised and normal and infarcted myocardium counted to see if disproportionately large numbers of platelets are trapped in the infarct and particularly at the infarct margin. BIBLIOGRAPHIC REFERENCES: Smith, G.T., Soeter, J.R., Haston, H.H. and McNamara, J.J.: Coronary reperfusion in primates. Serial electrocardiographic and histoligic assessment. J. Chin Invest 54:1420-1427, Dec. 1974.